MSTO2P and osteosarcoma: it is upregulated in patient samplespatients with low MSTO2P levels lived longer than those with high MSTO2P levelspatients with higher stages of osteosarcoma (stage III þ IV) showed higher expression levels of MSTO2Pknockdown of MSTO2P reduces cell growth, invasion, and EMT of osteosarcoma cells under hypoxia conditionsPD-L1 acts as a key effector for MSTO2P-regulated osteosarcoma progression under hypoxia conditionsMSTO2P positively influences the tumor growth in immunodeficient mice and in the human clinical tissues